On 6/12/25 6:37 AM, Vasant Hegde wrote:
Alejandro,
On 5/2/2025 7:45 AM, Alejandro Jimenez wrote:
Make amdvi_get_pte_entry() return an error value (-1) in cases where the
memory read fails, versus the current return of 0 to indicate failure.
The reason is that 0 is also a valid PTE value, and it is useful to know
If PTE is valid then at least PR bit will be set. So it will not be zero right?
I can change the wording in the last sentence to something like:
"The reason is that 0 is also a valid value to have stored in the PTE in
guest memory i.e. the guest does not have a mapping"
What I am trying to convey is that amdvi_get_pte_entry() should return
three different states:
-1: Error attempting to read the guest memory that contains the PTE i.e.
dma_memory_read() returned an error. This has likely nothing to do with
the guest and signals a problem with the emulation (e.g. problem with
QEMU memory backend)
0: The guest memory containing the PTE was successfully read, but there
is currently no mapping in that PTE i.e. *pte==0
>0: The guest memory containing the PTE was successfully read, and
there is currently a mapping i.e. *pte== <hopefully a valid IO page
table entry>
Before the change, amdvi_get_pte_entry() returned 0 for both an error
and for empty PTEs, but for the page walker implementation later in the
patchset we need to differentiate between those two conditions.
Thank you,
Alejandro
-Vasant
when a PTE points to memory that is zero i.e. the guest unmapped the
page.
Signed-off-by: Alejandro Jimenez <alejandro.j.jime...@oracle.com>
---
hw/i386/amd_iommu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index 5322a614f5d6..698967cc1a88 100644
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -496,7 +496,7 @@ static inline uint64_t amdvi_get_pte_entry(AMDVIState *s,
uint64_t pte_addr,
&pte, sizeof(pte), MEMTXATTRS_UNSPECIFIED)) {
trace_amdvi_get_pte_hwerror(pte_addr);
amdvi_log_pagetab_error(s, devid, pte_addr, 0);
- pte = 0;
+ pte = (uint64_t)-1;
return pte;
}
@@ -1024,7 +1024,7 @@ static void amdvi_page_walk(AMDVIAddressSpace *as, uint64_t *dte,
/* add offset and load pte */
pte_addr += ((addr >> (3 + 9 * level)) & 0x1FF) << 3;
pte = amdvi_get_pte_entry(as->iommu_state, pte_addr, as->devfn);
- if (!pte) {
+ if (!pte || (pte == (uint64_t)-1)) {
return;
}
oldlevel = level;
